It is highly desirable to be able to minimize the amount of service required for internal combustion engines to thereby minimize the interruption in the use of the vehicle/equipment. Degradation and contamination of engine lubricating oil during engine use requires oil changing procedures which account for a significant portion of the maintenance and associated engine "down time". Conventional periodic oil changes generate an accumulation of waste lubricating oil which must be disposed of and/or processed resulting in undesirable costs. Therefore, extending oil drain intervals and reducing waste disposal are of great value to vehicle/equipment operators.
Consequently, systems have been developed for automatically changing internal combustion engine crankcase oil during engine operation. For example, U.S. Pat. No. 3,447,636 discloses a system for automatically changing engine oil while the engine is operating. The system operates to drain substantially all of the used oil from the engine immediately prior to introducing fresh oil into the engine from a reservoir. The single operation process results in a complete change of the substantially the entire engine oil volume. However, draining the engine prior to refilling with fresh oil necessarily creates a risk that an inadequate supply of lube oil exists in the engine for an interim time period possibly resulting in damage or excessive wear to engine components from insufficient lubrication. Moreover, this system undesirably results in a quantity of waste oil.
Other systems have been developed which automatically change engine lube oil during engine operation while avoiding a waste quantity of oil by directing the used lube oil into the fuel system for burning with the fuel in the engine. These systems periodically drain a small amount of the used oil from the engine lube oil system, and replace the drained quantity with fresh lubricant from an auxiliary tank. For example, U.S. Pat. Nos. 4,869,346 and 5,390,762 to Nelson disclose an automatic crankcase oil change and makeup system including a displacement unit having a piston with a predetermined stroke set to deliver identical, predetermined amounts of fresh oil during each stroke at the same flow rate and volume as the extraction of used oil. The pressure of the used lubricating oil is used to cause the periodic addition of the fresh oil to the crankcase. The frequency of the pressure strokes is set by a timer in an electronic controller, and is adjustably set to stroke at fixed time intervals to provide a cumulative quantity of fresh oil to the crankcase according to the regular recommended oil change period for the particular engine. A pair of dials on the controller enable the frequency of the pressure strokes to be adjusted. However, during certain engine operating conditions, e.g. idle conditions, the engine lube oil supply pressure may too low to overcome the biasing force of the piston spring, an outlet check valve biasing pressure and any frictional counterforces. As a result, the piston may not be moved through its makeup stroke during certain engine operating conditions, thereby preventing oil replacement and makeup during these low pressure conditions.
U.S. Pat. Nos. 4,421,078; 4,495,909; and 5,431,138 to Hurner disclose similar systems for oil changing and making up during engine operation which include a control module having an adjustable impulse timer set to periodically cycle an air pressure operated oil extractor pump at a fixed time intervals to direct a predetermined amount of engine oil out of the oil pan and into the fuel tank. Fresh makeup oil is pumped from an oil reservoir to the crankcase, also by air pressure, in response to a low level signal from a dipstick sensor. However, the oil changing portion of each of these systems is formed as a separate assembly from the make-up portion of the system. Also, these systems require the use of pressurized air to actuate the oil changing/removing device. As a result, this system may be difficult and expensive to integrate into an engine.
U.S. Pat. No. 4,417,561 to Yasuhara discloses an automatic oil changing and disposing apparatus wherein used crankcase oil is periodically directed to a fuel tank via a valve controlled by an odometer switch, and fresh oil is gravity fed from a fresh oil tank to the crankcase via a control valve controlled by a crankcase oil level switch. The quantity of each increment of used oil removed from the crankcase, and each increment of fresh oil supplied, is controlled by respective timers having variable on-time duration to effect variable control of engine oil extraction and addition. Alternatively, a float type valve arrangement can be used to control the delivery of the fresh oil to the crankcase. However, in the systems disclosed in the Hurner references and Yasuhara, fresh oil may be delivered to the crankcase during engine operation after significant amounts of used oil have been removed and only when the fresh oil tank level drops a predetermined low level. This undesirable delay in supplying fresh oil to the engine results in a significant decrease in the quantity of lubricating oil in the lubricating oil system of the engine thus creating the possibility that too little oil will be available to the engine. Moreover, the repeated extraction of used oil without periodic, corresponding additions of fresh oil, fails to adequately maintain the quality of the lubricating oil in the engine at a sufficient level to ensure optimum engine lubrication and cooling.
Although capable of automatically changing lube oil during engine operation, the automatic oil changing systems discussed hereinabove are incapable of accurately varying and controlling oil changing in response to the actual needs of the engine that vary based on the engine operating conditions, such as fuel consumption. The amount of oil drained from the crankcase and injected into the fuel system is often either less than the necessary replacement rate when the engine is being used more heavily than expected, or more than the optimum amount when the engine is being used less heavily than expected. Injecting too little used oil from the oil sump into the fuel system will disadvantageously result in engine damage from over-used oil incapable of adequately lubricating and cooling engine components. On the other hand, injecting too much oil results in excessive concentrations of used oil in the fuel resulting in engine performance degradation, increased emissions, shortened fuel filter life and wasted oil. In addition, if the engine is a recent emission regulated engine, injecting too much oil into the fuel system will result in emission non-compliance and possibly a fine. Although Yasuhara '561 suggests variable control of engine oil extraction and addition, this reference does not suggest means for accomplishing such variable control nor the engine operating parameters to be considered. The Nelson '346 and '762 references only suggest varying the amount of oil extracted and added to the engine crankcase by manually adjusting timers to vary the frequency of oil additions and extractions.
Also, the systems discussed hereinabove fail to adjust the quantity of oil to be injected from the lube oil system into the fuel system based on the amount of additional fresh oil added to the oil sump beyond the quantity extracted. For example, the systems disclosed in the Nelson patents operate to deliver an amount of fresh oil, during each stroke of the displacement unit, to replace the amount of used oil removed. The Nelson system also operates to deliver additional amounts of fresh oil when the oil sump level decreases below a predetermined level due to, for example, oil leakage or burning in the engine. However, the Nelson system continues to remove and replace oil at a predetermined frequency. As a result, these systems replace more oil than is necessary to maintain cooling and lubricant qualities of the oil at the desired level, resulting in wasted oil and increased costs.
Therefore, there is a need for a continuous engine lube oil replacement system capable of more effectively controlling the quantity of used lube oil burned in the engine based on varying engine operating conditions.